Artificial radiation sources have been recognized to radiate a large amount of radioactive rays in comparison to natural radiation sources. For example, the exposure dose by one-time X-ray scanning corresponds to the exposure dose by natural radiation for one year in some cases.
Despite this circumstance, medical use of radiation is socially accepted because in many cases the use of radiation is inevitable in order to treat patients. Radiation treatment should be justified on the basis of EBM (Evidence Based Medicine) and should obey limitations for as low exposure dose as possible within a range of obtaining useful medical information together with optimization against radiation.
Existing film type of diagnostic X-ray systems measure an X-ray dose using an ion chamber installed at the front end of a film to measure an X-ray dose.
However, such an ion chamber has a complicated structure due to a plurality of electrodes and is difficult to reduce in size, so there is a need for installing expensive equipment ahead of a detector.
Recently, not the film type, but a CCD type or flat panel type X-ray detector (hereafter, referred to as an “FPD”) has been used. The FPD has a sensing membrane on a substrate, and detects radiation reaching the sensing membrane, converts the detected radiation into charge, and accumulates the charge in a capacitor having two-dimensional array. The accumulated charge is sensed when a switching device is turned on and transmitted as a radiation detection signal to a image processor. The image processor obtains a radiograph having pixels based on the radiation detection signal.
Using the FPD makes it easy and simple to keep and process a radiograph without complicated distortion in detection, as compared with the film type used in the related art. Therefore, the FPD is advantageous in terms of the structure of the system and image processing.
However, when an image system including the FPD is used to radiograph an object, the larger the tube voltage (kVp) and the radiation dose (mAs), the larger the exposure dose to the object.
In contrast, when the tube voltage (kVp) or the radiation dose (mAs) is reduced, the luminance of a radiograph obtained by the FPD is reduced, so it is difficult to interpret the radiograph.
Therefore, there is a need for X-ray radiograph that minimizes the exposure dose to an object and provides an appropriate luminance for a radiograph obtained by the FPD.
According to the film type in the related art, an ion chamber needs to be disposed ahead of a detector to measure an X-ray dose and it is required to adjust the conditions for X-ray radiography in accordance with the amount of X-ray radiated to the ion chamber. On the other hand, according to a CCD type or a flat panel type in which an ion chamber actually cannot be installed, radiography is performed on the basis of radiograph conditions including the tube voltage (kVp) or the radiation dose (mAs) of an X-ray type, and for this purpose, a lookup table (LUT) about each part to be radiographed of an object so that an operator determines radiography conditions in consideration of the sex, age, and weight on the basis of the lookup table.
Accordingly, the CCD type or the flat panel type of the related art do not use the way of obtaining an optimal radiograph with the minimum exposure dose by precisely determining the tube voltage and the radiation dose (mAs) in accordance with the physical features of an object, but depends on only on an operator's skill based on experience in radiographing an object.
There has been proposed a “Radiation imaging apparatus” for radiographing an object in Korean Patent Application No. 10-2010-0022618. The apparatus includes: an electromagnetic ray generator that radiates a plurality of electromagnetic rays to an object using a plurality of electronic sources arranged in a one-dimensional or two-dimensional array; an electromagnetic ray detector that obtains a plurality of first radiographs by detecting electromagnetic rays that are radiated through an object at different angles when the apparatus is in operation; an area specifier that specifies an area on an object using the first radiographs obtained by the electromagnetic ray detector; and a determiner that determines an electronic source to be operated of the electronic sources on the basis of the area on the object specified by the area specifier, in which a second radiograph is obtained by the electromagnetic ray generated by the electronic source determined by the determiner. According to this mammography system that is used for radiographing breasts, the luminance of an area on an object is determined on the basis of a first radiograph obtained through a pre-shot process, which radiates an X-ray in advance, and then a corresponding main-shot is actually radiated in order to obtain an appropriate radiograph having a desired luminance of breast tissues because objects have different breast tissues and sizes.